Inclusion Criteria:
1. Age and Informed Consent: The age range is 18 to 75 years (inclusive), and the participant must voluntarily participate in this study and sign the patient informed consent approved by the ethics committee.
2. Pathological Diagnosis: Gastric or gastroesophageal junction (GEJ) adenocarcinoma confirmed by histological or cytological examination.
3. Disease Staging: Newly diagnosed, unresectable stage IV disease (according to the 8th edition of the AJCC staging system), confirmed by the multidisciplinary team (MDT) of the research center to be unable to undergo radical surgical resection. The types of metastasis include but are not limited to: unresectable distant lymph node metastasis (such as beyond the abdominal aorta trunk, supraclavicular lymph nodes, etc.); distant organ metastasis (such as liver, lungs, peritoneum, ovaries, etc.).
4. Conversion Therapy and Efficacy:
1. Has received 4-6 cycles of first-line standard conversion therapy. The treatment plan should be based on the latest clinical guidelines and molecular typing (such as fluorouracil/platinum double or triple drug chemotherapy, combined with anti-HER2 treatment (for HER2-positive patients) or immune checkpoint inhibitors (PD-1/PD-L1 inhibitors, such as when CPS ≥ 5 or MSI-H, etc.).
2. After conversion therapy, according to the RECIST 1.1 standard, confirmed by the independent imaging assessment committee (IRC) or at least two senior radiologists, the efficacy reaches complete response (CR) or partial response (PR).
5. Surgical Feasibility Assessment: Re-evaluated by the MDT of the research center (must include senior gastrointestinal surgeons, oncologists, and radiologists), it is considered that all known lesions (primary and metastatic lesions) can be technically achieved R0 resection, and the patient is expected to be safely and tolerably able to undergo surgery.
6. Physical Condition: Eastern Cooperative Oncology Group (ECOG) performance status score (PS) of 0 or 1.
7. Good Organ Function (measured within 14 days before randomization), meeting the following laboratory test value standards:
1. Hematological System:
Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L Platelet count (PLT) ≥ 100 × 10⁹/L Hemoglobin (Hb) ≥ 90 g/L
2. Liver Function:
Serum total bilirubin (TBIL) ≤ 1.5 times the upper limit of normal (ULN) Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN (if liver metastasis, then ≤ 5 × ULN)
3. Renal Function:
Serum creatinine (Cr) ≤ 1.5 × ULN, or creatinine clearance rate (Ccr) ≥ 50 mL/min (Cockcroft-Gault formula)
8. Female patients of childbearing age must have a negative serum pregnancy test within 7 days before randomization, and all patients (regardless of gender) must agree to take effective contraceptive measures during the study and within 6 months after treatment.
Exclusion Criteria:
1. Pathological type: Other pathological types, such as squamous cell carcinoma, adenosquamous carcinoma, undifferentiated carcinoma, gastrointestinal stromal tumor (GIST), etc.
2. Treatment and efficacy:
1. During the conversion therapy, disease progression (PD) was confirmed after assessment.
2. Previously received systemic anti-tumor treatment for advanced gastric cancer (except for conversion therapy).
3. Previously received radical radiotherapy for the stomach or metastatic lesions.
3. Surgical contraindications:
1. According to MDT assessment, there are residual lesions that cannot be surgically removed (such as diffuse peritoneal metastasis that cannot achieve satisfactory tumor reduction, extensive liver metastasis that cannot preserve sufficient functional liver tissue, etc.).
2. There are severe internal medical comorbidities that significantly affect surgical safety, and the anesthesiology and surgical physicians have evaluated that the surgical risk is extremely high, for example:
Uncontrolled heart failure (NYHA cardiac function class III-IV), unstable angina or myocardial infarction within 6 months.
Severe chronic obstructive pulmonary disease (COPD) or other severe respiratory diseases, which are expected to be intolerant to general anesthesia.
Uncontrollable severe infection.
4. Past and coexisting disease history:
1. In the past 5 years, had other active malignant tumors, except for cured skin basal cell carcinoma, cervical carcinoma in situ, etc.
2. Had any uncontrolled severe clinical problems (such as severe mental or neurological diseases) that affected the compliance with the protocol or interfered with the interpretation of the research results.
5. Laboratory test abnormalities: Any serious and uncontrolled laboratory test abnormalities were found. The investigator considered that participating in this study would bring significant risks.
6. Pregnancy and lactation: Pregnant or lactating women.
7. Other: Known to have a severe allergic history to any drugs (chemotherapy drugs, targeted drugs, immunotherapies, anesthetics, etc.) used in the study protocol. The investigator believed that there were any other situations that were not suitable for participating in this clinical study.
